1. Field of the Invention
The present invention relates to an exposure apparatus including a vacuum chamber.
2. Description of the Related Art
A method of producing a minute semiconductor device such as a logical circuit or a semiconductor memory using photolithography techniques is known. In this method, a circuit pattern, formed on a reticle (mask), is projected and transferred onto a substrate, such as a wafer, using a reduction projection exposure apparatus.
A minimum size (resolution) that can be transferred in the reduction projection exposure apparatus is proportional to the wavelength of exposure light, and is inversely proportional to the numerical aperture (NA) of a projection optical system. Therefore, the shorter the wavelength, the higher the resolution. Consequently, a demand for minuter semiconductor devices in recent years is reducing the wavelength of exposure light that is used. For example, exposure light having wavelengths that are shorter than those of an i line (λ=approximately 365 nm) of an ultra-high pressure mercury lamp, KrF excimer laser light (λ=approximately 248 nm), and ArF excimer laser light (λ=approximately 193 nm) is used.
However, since semiconductor devices are rapidly becoming minuter, lithography techniques using ultraviolet light has limitations. Therefore, to efficiently transfer a very minute circuit pattern of 0.1 μm or less, a reduction projection exposure apparatus (EUV exposure apparatus) using extreme ultraviolet light (EUV light) having a wavelength λ of approximately 10 to 15 nm, which is shorter than that of ultraviolet light, is being developed.
Since, in the wavelength range of the EUV light, attenuation of energy due to gas is extremely large, a vacuum needs to be produced in the exposure apparatus. In addition, since impurities and oxygen in the gas may adhere as carbon compounds to an optical element due to photochemical reaction, partial pressure of the carbon compounds in the exposure apparatus needs to be low. The partial pressure of the carbon compounds needs to be very low particularly in a projection optical system space.
PCT Japanese Translation Patent Publication No. 2002-529927 (corresponding to U.S. Pat. No. 6,198,792) discloses a technology for preventing the flow of carbon compounds into a projection optical system space. More specifically, it discloses a method of restricting the flow of carbon compounds from a stage space by maintaining the pressure in the projection optical system space higher than that around the projection optical system space as a result of forming another space by surrounding the projection optical system space by a plate.
To maintain the pressure in the projection optical system space higher than that around the projection optical system space, gas needs to be supplied to the projection optical system space. The gas may be supplied to the projection optical system space by supplying the gas using a nozzle from outside an apparatus through a pipe. However, when atmospheric-pressure gas is supplied to a space whose pressure is equal to or less than 100 Pa, even if an orifice or an aperture is formed in the pipe, the gas flows into the projection optical system space at a considerably high flow rate. Therefore, vibration occurs in the pipe. When, in such a state, the pipe is directly joined to a partition defining the projection optical system space, the vibration of the pipe is transmitted to the projection optical system, thereby reducing the precision with which a pattern is transferred.
When, to prevent the vibration of the pipe from being transmitted, the pipe and the partition defining the projection optical system space are simply separated from each other so as not to contact each other, the amount of gas leaking from a gap between the pipe and the partition is increased. As a result, it is difficult to set the pressure in the projection optical system space higher than that around the projection optical system space.